I've installed version 1.1.4 from this Customisation Database and tried to run it on phpBB 3.2.2 board (php 5.6.30, MySQL(i) 5.5.34). This extension hasn't been installed before. When I tested it on my localhost test server with phpBB 3.2.2 it worked without problems.

Did you have the mod, not extension...mode from 3.0 days, installed before? Try to uninstall and delete date of the extension.

In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists - Eric HofferFormer Modifications/Extensions Team Member | My extensions
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No, as far as I know. But the DB itself is 10 years old so I can't say for 100 % that it doesn't contain any remaining data if it was installed in the past. I'll try to reinstall the extension ASAP, but I'm worried the dog is burried elsewhere…

If uninstalling and deleting data doesn't fix it then you will have to go into the database and remove contactadmin_enable from the config table. Once you do that purge the cache and you should then be able to install and use the extension.

In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists - Eric HofferFormer Modifications/Extensions Team Member | My extensions
Appreciate the extensions/mods/support then buy me a beer
All requests for support via PM will be ignored

Hmm, it seems the problem has been solved somehow. I've re-enabled the internal phpBB Contact admin formular (after it was disabled by the extension), deleted extension's data, enabled it and now it seems to work.

In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists - Eric HofferFormer Modifications/Extensions Team Member | My extensions
Appreciate the extensions/mods/support then buy me a beer
All requests for support via PM will be ignored